This invention relates to a superconductor covered with a reinforced aluminum matrix and to a method for the manufacture thereof. More particularly, the present invention relates to a superconductor covered with an aluminum matrix which makes the most of the high electric conductivity, the high thermal conductivity and the magneto resistance effect saturation characteristic inherently exhibited by high-purity aluminum at very low temperatures in an extremely high magnetic field and tensile strength and enjoys a notably improved tensile strength such as has heretofore been found difficult to attain by the prior art and to a method for the manufacture of said aluminum superconductor.
As is universally known, a superconductor has a thermal conductivity on the order of 10.sup.-3 to 10.sup.-2 W/cm.deg. which is so low that when an electric current of high current density flows superconductively through said superconductor, the superconductor generates heat due to magnetization, magnetic flux jump or some other cause. Consequently the superconductor transiently or partially shifts to a normally conductive state. Because of this phenomenon, there has been suggested a method for stabilizing the behavior of the superconductor by cladding said superconductor with a normally conductive metal possessed of high electric conductivity and high thermal conductivity. To date, copper of high purity has been used preponderantly as the normal conductive metal. Copper, however, has a disadvantage that the electric resistance thereof increases notably in proportion the magnetic field.
In contrast, aluminum of high purity has its electric resistance increased in a high magnetic field to only about twice the value in an absence of magnetic field. It enjoys the saturation characteristic that the electric resistance no longer varies even if the magnetic field is intensified further. Moreover, aluminum excels copper in electric conductivity and thermal conductivity and has light weight. Thus, aluminum possesses outstanding characteristics as the normal conductive metal. When aluminum of high purity is deposited to directly clad superconductors such as, for example, of an Nb-78% Ti wire and the clad wires are subjected to wire-drawing, because of a broad difference in hardness between the two metals, there ensues a flowing phenomenon wherein only the aluminum layer on the surface is drawn out. Thus, the desired integral forming of the two metals cannot be obtained by co-drawing. Formerly, the present inventors proposed an aluminum clad multiplex superconductor having a uniform cross-sectional distribution of components throughout the entire length by precluding the flowing phenomenon which would otherwise occur while an aluminum clad multiplex superconductor was undergoing wire-drawing (U.S. Pat. Nos. 3,714,371 and 3,778,895). According to the invention of said U.S. patents, the aluminum clad multiplex superconductor is obtained by placing at least three twisted or braided superconductive wires inside a pipe of highly pure aluminum, sheathing said aluminum pipe with a pipe of an aluminum alloy having a Vickers' hardness of not less than 50 and subjecting the resultant composite cable to the wire-drawing, whereby the superconductive wires and the aluminum pipe are integrally drawn out and brought into intimate mutual cohesion. The wire-drawing to be performed on the aluminum pipe and the superconductive wires during the aforementioned manufacture of the aluminum clad superconductor, however, necessitates highly advanced skill. Further, the manufacture of said aluminum clad superconductor necessitates use of at least three twisted superconductive wires.
The object of this invention is to provide a superconductor covered with a reinforced aluminum matrix which makes the most of the high electric conductivity, the high thermal conductivity and the magneto resistance effect saturation characteristic inherently exhibited by aluminum of high purity at very low temperature and enjoys a notably improved tensile strength and also a method for the manufacture of said aluminum clad superconductivity of high tensile strength.